B0_driver.EnvSourceDriver environment variables.
b0_dir is the variable used to specify the b0 directory.
b0_file is the variable used to specify the b0 file to use.
cache_dir is the variable used to specify the b0 cache directory.
color is the variable used to specify tty styling.
code is the variable used to specify the code to which the driver compiles to.
hash_fun is the variable used to specify the cache hash function.
jobs is the variable used to specify the maximal number of spawns.
verbosity is the variable used to specify log verbosity.